NBSIR 73-276 0<)

Standards for Athletic Helmets —

State of the Art and Recommendations

Bal M Mahajan

Consumer Product Systems Section

Measurement Engineering Division

Institute for Applied Technology

April 1, 1974

Final Report

Prepared for Consumer Product Safety Commission

5401 Westbard Ave.

Bethesda, Maryland 20016

NBSIR 73-276

STANDARDS FOR ATHLETIC HELMETS -- STATE OF THE ART AND RECOMMENDATIONS

Bal M. Mahajan

Consumer Product Systems Section

Measurement Engineering Division

Institute for Applied Technology

April 1, 1974

Final Report

Prepared for Consumer Product Safety Commission

5401 Westbard Ave.

Bethesda, Maryland 20016

U. S. DEPARTMENT OF COMMERCE, Frederick B. Dent, Secretary

NATIONAL BUREAU OF STANDARDS, Richard W. Roberts. Director

Table of Contents

Page

Introduction 1

Impact Induced Head Injuries , , 2

General 2

Type, Mechanism and Relative Severity of Head Injuries 3

Injury Criteria and Threshold Limits 8

Present Standards 11

Performance Criteria for Athletic Helmets 13

Concluding Remarks 16

References 17

il
t Abstract

The literature concerning impact-induced head injuries was

surveyed for information on types of head injuries, their

relative severity, and injury threshold values. The search

revealed that threshold values are either questionable or not

available

A review of standards for helmets revealed that there are no

satisfactory performance standards for athletic helmets and that

performance criteria and testing procedures used to evaluate

other helmets may be neither appropriate nor adequate for testing

athletic helmets.

Necessary information is suggested for developing

performance criteria and test procedures for athletic helmets.

Studies to acquire such information are recommended. Since some

of these are complex and may take a long time to complete,

interim performance standards for athletic helmets should be

developed using current information, and these standards should

be revised as the state of the art advances.

iii
standards for Athletic Helmets — State of the Art

and Recommendations

Introduction

Wearing helmets to prevent or mitigate head injury is not

new. Protective headgear has been in use since ancient times,

principally in war. Recently, protective helmets have found wide

general use, especially in athletic games such as football,

hockey, and baseball. In responding to increased participation

by both children and adults in body-contact games, manufacturers

have produced many protective helmets whose effectiveness may be

questionable. Protective helmets are virtually mandatory in

body-contact athletics, but performance standards for the

protection offered by such helmets are almost non-existent. The

National Commission on Product Safety indicates that football

players in the United States suffer annually 250 000 to 500 000

brain concussions during play [62], emphasizing the need for

performance criteria and test methods to evaluate athletic

headgear.

To develop performance criteria and test methods, one should

know the maximum acceptable impacts transmitted to the head

through the helmet and the impact conditions that are generated

by athletic mishaps. The maximum acceptable impacts transmitted

to the head depend on the type and severity of head injuries

which are acceptable. Information on impact-induced head

injuries is essential. This information includes: (1) the type,

mechanism, and relative severity of head injury likely to result

when the human head is subjected to impact loads, and (2) the

various criteria which are used to define impact tolerance

limits, or injury threshold values, and the injury threshold

values for different head injuries.

It is the purpose of this report to survey the literature

concerning impact-induced head injuries, to review existing

performance criteria and test methods for headgear, and to

recommend studies which will supply the base for developing

effective performance criteria and test procedures for athletic

helmets
Impact-Induced Head Injuries*

General

During the past three decades much research has concentrated

on Injuries to the human body subjected to Impact loads. Head

Injuries have received more attention than Injuries to any other

part of the body, probably because of the vulnerability of the

head to Impact Injuries and a high correlation between head

Injury and death.

Some of the factors known to Influence head Injury due to

Impact are the geometry and mechanical properties of the Impacted

surface, biophysical properties of scalp and skull, amount of

hair on the head, region of the head. Impact direction and

Intensity (velocity, momentum, or energy), the magnitude,

distribution, direction, and duration of the resulting force, and

the whole body orientation. In addition, physiological factors

such as age, sex, and physical and mental condition of the

Individual are thought to affect the outcome of accidents,

although the manner of their Influence Is not completely

understood.

Several techniques have been used to explore the mechanism

of head injuries, including experiments with cadavers,

experiments with animals, and experiments with inanimate forms

simulating human and subhuman heads. Different researchers have

reached different conclusions concerning head injury mechanisms,

especially for internal head injuries [1] to [20]. However, most

researchers agree that head injuries are usually caused by a

combination of mechanisms and that, depending primarily upon the

Impacting conditions, any one mechanism may contribute more to

the overall damage than the others [21]. A discussion of head

injury mechanisms and a list of references can be found in [5].

*The information presented in this section is obtained from the

literature pertaining to impact injuries. Over 150 articles

and papers were consulted; only the more appropriate ones are

cited.

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Impact tolerance has been variously defined, and different

investigators have used different criteria to establish injury

threshold values [22 ] to [^13]. Mechanical quantities used in

these criteria to define tolerance limits or injury threshold

values include impact velocity, momentum and energy, energy

absorbed, impact force, effective contact area, impact duration,

impulse, impulse divided by head mass (specific impulse),

weighted impulse (Severity Index [24]), acceleration (both

translat ional and rotational), change in head momentum or

velocity. Jerk, and induced pressure or pressure gradient.

Most of the critiera developed so far have limited

application because of the great variety of head injuries, the

variability of skull shape and other properties of the head from

person to person, and the large number of probable impact

conditions. There are some criteria, however, such as the WSU - Tolerance Curve [3 9], [28] and Severity Index, which have found

widespread use despite all these limiting factors.

The data used in most of these developments came from

clinical reports of accidents and the laboratory experiments

mentioned above. Tolerance limits and threshold values so

established may always be questionable, because (1) the data from

clinical reports, estimated after the event, may not be reliable

and (2) the experimental models (cadavers, living animals, and

Inanimate forms) do not have the same biophysical and

physiological characteristics as those of the live human. At the

present state of the art, it is not feasible to establish

tolerance limits and threshold values using live humans.

Type, Mechanism, and Relative Severity of Head Injuries

Possible head injuries resulting from impact loads are scalp

injuries, skull fractures, and internal head or brain injuries.

(Figure 1 shows the schematic anatomy of the human head.)

Scalp injuries can be divided into five types, described

below in increasing order of severity:

1. A bruise (contusion) is damage to the soft tissue and

small blood vessels that does not break the skin. It occurs

when a compressive Impact causes the small blood vessels

beneath the skin to force ( extravasate ) blood into the

surrounding tissue under the intact skin.

2. An abrasion is caused by a blunt object sliding over the

scalp with sufficient force to remove the superficial

layers of the skin.

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3. A puncture occurs when a sharp (pointed) object impacts

the skin with sufficient force to penetrate it.

^. A laceration is an Incised wound which usually occurs

when a sharp object (a sharp edge or a sharp point) pressing

against the skin is pulled across it.

5. An avulsion results when the peeling action of an impacting

object rips off a portion of the scalp from the skull.

Scalp injuries are quite common, especially when the head is

bare when impacted, and may result in severe hemorrhage.

Infection, or disfigurement. Even so, they are not as

potentially lethal as are skull and brain injuries.

Skull fractures may be either closed or open, A closed

fracture is a break in the skull with no apparent break in the

overlying scalp. In an open fracture both the skull and the

overlying scalp are broken. Open fractures are more serious than

closed ones because the open fractures may become infected, and

infection may complicate the healing process.

Skull fractures are of four major types: linear, indented,

depressed, and crushed. The first three types are not life

threatening if not accompanied by brain damage,

1, A linear fracture usually results from head impact

with a relatively blunt object (contact area in the range

of two square inches or larger) [32], It occurs when the

applied load, acting on a section of the skull, produces

a large enough bending moment to crack the bone. Because

of the biological variations in skulls, the exact configuration of the crack cannot be predicted with certainty. Usually it appears as a single line emanating

from the area of impact and may involve either the inner

or outer skull surface or both [1], Sometimes, however,

linear fracture appears as a stellate fracture, a group

of cracks in a star shape radiating from the central

impact point. Another form of linear fracture is the

basal fracture which results when the impact energy from

a blow to the cranial vault is transmitted around the

skull to cause fracture in the area of the foramen magnum.

Sometimes a linear fracture perpendicular to the path of

a meningeal artery may rupture the artery and cause a

blood clot on the main surface (epidural hematoma), a

life-threatening injury,

2, In an indented fracture the skull is displaced inwardly

I
without a fracture line being visible. It occurs mainly

In children whose skull bones are thin and flexible.

Complications may include brain compression and disfigurement .

3. Depressed fractures are of two kinds, penetrating and

comminuted.

Penetration-type depressed fractures are the result of

highly localized loading of the skull by an insulting

object with an impact area less than one square inch [32].

The failure appears directly under the impactor on the

outer surface of the skull, usually as the impactor

punches out, by shearing action, that portion of the skull

directly under it, with little or no disturbance of the

surrounding skull [1], [32].

Comminuted depressed fracture generally occurs when an

impactor, having an impact area in the range of one

to two square inches, causes a localized indentation of

the skull and breaks the depressed bone into several pieces

[32]. The larger impact area generally precludes skull

penetration; instead, the skull in the vicinity of the

impacted region deforms as a structural unit, producing

a concentrated bending moment in the skull directly

under the load region causing the bone to fail. Broken

fragments of the bone may be driven into the interior

of the head causing internal injuries.

4, A crush fracture occurs when the head is caught in a

vise-like action, such as when a car rolls over a

victim's head. Crush fractures usually result in death.

This type of fracture is not likely to result from

foreseeable athletic mishaps.

In general, skull fracture is an indication of severe

impact. There are conditions, however, under which fatal impacts

to the human head may not cause skull fracture. For example, if

the impact loading is distributed over the skull (a desirable

condition for fracture mitigation, and one of the functions of a

protective helmet), a fatal internal head injury can result

without skull fracture [5].

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Internal Head or Brain Injuries

Internal head or brain Injuries are much more serious than

scalp and skull Injuries [1] and consequently are the most

important to be protected against. The types of brain Injuries

to be discussed are cerebral concussion, and brain contusion,

laceration, and Intracranial bleeding, of which concussion Is the

most common.

The mechanisms of brain Injury have been a subject of

controversy among researchers, who have concentrated on different

mechanical causes. Including: linear and rotational

acceleration, deceleration, compression, changes In Intracranial

pressure, cavitation In the area opposite to the site of Impact

(countrecoup) , and relative motion of the brain with respect to

the skull.

Detailed descriptions of brain Injuries and braln-lnjury

mechanisms can be found In references [5] and [l8]. The

following are simplified descriptions of the brain Injuries

mentioned above.

1. Cerebral concussion may be described as an Immediate posttraumatic brain dysfunction characterized by unconsciousness

and blindness or Inability to focus which Is usually

reversible but may be fatal [5]. In closed-head

Injury, concussion Is generally considered to be due to

the stretching of the brain stem. [A direct blow to the

head causes the skull and brain to move In a direction

determined primarily by the location and direction of the

blow. The brain lags behind the skull, causing a relative

motion between the skull and brain which allows the main

cerebral mass to move (translate or rotate) with respect

to the brain stem. The relative motion between the brain

and brain stem produces stretching of the brain stem.]

However, the mechanisms responsible for long periods of

unconsciousness, which accompany severe concussion, have

not been definitely established. In severe concussion,

extensive diffuse cerebral damage Is usually found; thus

stretching of the brain stem may not be solely responsible.

Furthermore, direct Impact of the head Is not the only

way In which a concussion Is produced. It Is known that

a concussion may also be produced by a whiplash [1], [16],

A concussion with loss of consciousness for up to 30

minutes Is considered to be serious but not lifethreatening; a concussion with unconsciousness lasting

more than 30 minutes Is considered to be llfe-threatenlng.

-6-
2. Relative movements of the brain with respect to the skull

are due to different rates of acceleration of the skull and

brain follov/lng Impacts. These movements are the usual cause

of brain contusion . Brain contusions occur not only In the

si te-of- Impact Tcoup) and opposlte-to-the-impact (contrecoup)

regions, but may be sufficiently v;ldespread to constitute

a form of diffuse brain damage.

The relative motion between the skull and brain produces

injury to the brain as well as tearing of the blood vessels

that connect the brain to its overlying membranes, causing

intracranial bleeding (subdural hematoma). Subdural bleeding

following a head injury in sports is potentially lethal [5],

[7], [9].

In the region of the Impact, pressure from the blow may cause

the small blood vessels to burst and force (extravasate)

blood into the surrounding tissue.

In the region opposite the impact site, the mechanism of

injury is more complex. One theory holds that the skull

being more rigid than the brain, is driven in the direction

of the blow with the contrecoup point traveling nearly as

fast as the coup point, while the brain deforms and lags

behind the skull. Under these conditions a positive pressure

at the coup point and a negative pressure at the contrecoup

region are developed. The negative pressure causes the

formation of bubbles in and on the brain substance; brain

damage results during both formation and collapse of the

bubbles [5].

Subdural and subarachnoid hemmorhages (see Fig. 1) have been

observed in athletes who have suffered severe head injuries

during baseball and football. In many cases of fatal boxing

injuries, large subdural hematomas are seen [7]. A frequent

pathological finding is the presence of hemmorhages in the

brain stem. These may be secondary to pressure against or

other injury to the brain stem or to primary lesions

caused at the time of Impact by shear strains in the brain

stem which result from pressure gradients [51.

Brain laceration occurs when the brain is subjected to a

force of sufficient intensity to cause tearing of the brain

substance. Brain laceration, when accompanied by skull

fracture, can be produced by broken bone fragments that are

driven into the brain substance.

These injuries (brain contusion, brain laceration, and intra-

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cranial bleeding), based on clinical prognosis, may be

different levels of severity. However, all of them are

life-threatening, and for the purpose of this report they

are placed at the same level of severity.

Table 1 shows In summary form the various types of ImpactInduced head Injuries and their relative severity.

Injury Criteria and Threshold Limits

Some of the criteria that have been used to define or

establish threshold limits for the three major categories of head

Injuries are given below.

Scalp Injuries have received the least attention of all the

head Injuries, and relatively little has been done to establish

scalp injury threshold limits. Gadd et al. [23] obtained limited

data for the laceration and crushing of the scalp and related

their data to impact force and the geometry of the impacting

object. Others [^^] to [^6], studying the resistance of skin to

puncture and laceration under mostly static loading, also used

the applied force and the geometry of the insulting object in

their analysis.

From the limited data of references [23], [^^], [^5], and

[46], the following injury threshold values can be estimated:

The scalp contusion threshold is approximately 500 lbf/in^(3.5 x lO^N/m^). The scalp puncture and/or laceration threshold ranges

from 1300 Ibf/ln^ to 10 000 Ibf/ln^ (9 x 10^ to 69 x 10^ N/nf )

,

depending upon the geometry of the injuring object and the

biophysical properties of the scalp.

No data have been found on abrading and avulsion of the

scalp.

Some of the criteria or combinations of different ohysical

factors which have been used to establish skull fracture

tolerance or threshold values are: (1) peak Impact force and

effective contact area, (2) peak Impact force and the geometric

description of the impacting object, (3) energy absorbed, (4)

acceleration (peak or average) and effective contact area, (5)

average or effective acceleration and time duration, as In the

Wayne State University acceleration-time tolerance curve (WSUcurve) [28], (6) Severity Index (S.I.), and (7) Effective

Displacement Index (EDI). The last three of these, however, were

originally proposed for life-threatening cerebral concussion.

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The numerical values obtained for skull fracture threshold

limits range widely, primarily because the outcome of Impact

depends upon the region of skull Impacted, the geometry of the

Impacting object and the biophysical properties of the skull and

overlying scalp, which vary from individual to individual.

Threshold values for skull fracture and other injuries and

the appropriate references are presented in Table 2.

The most frequently used criteria for defining the threshold

values for Internal head InJ ury are the follov^lng: WSU-curve

[28], S.I. [24] , EDI [22], Maximum Strain Criterion Tolerance

Curve (MSC) [40], J-Tolerance Value of the Vienna Institute of

Technology [38], and the National Highway Traffic Safety

Administration's Head Injury Criterion (HIC) [48].

The WSU-curve , for cerebral concussion due to frontal

Impacts, was constructed by combining data from intracranial

pressure studies, cadaver skull fracture tests, and volunteer

sled riders [7], [28]. The tolerance data are presented as a

curve on rectilinear graph paper with effective acceleration

(area under the computed acceleration pulse divided by the pulse

duration) as abscissa and pulse duration as ordinate. From this

curve, cerebral concussion threshold limits can be obtained in

terms of effective acceleration of the head and pulse duration

(See table 2).

The severity index is defined as

S.I. = ^^^^^^^^ (seconds) (1)

where: g = 9. 806 65 meters per second squared,

a = acceleration in the units used for gj^ .

m = weighting factor greater than one (2.5 has been used for

internal head injury),

tQ = starting time of the acceleration pulse in seconds.

t f> = final time of the acceleration pulse in seconds.

The method for computing the S.I. from the acceleration-time

record of any pulse is found in references [39] and [4?]. A

value of S.I. = 1 000 seconds has been proposed as the threshold

value for life-threatening Internal head injury.*

Although the units of S.I. and HIC are seconds, the units are

almost always omitted in the literature.

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The EDI tolerance values are obtained by computing the

maximum displacement of the mass In a mathematical head-damage

model, when the model Is excited by an impulse applied to its

base. The model is a single-degree-of-freedom, damped springmass system represented by a second-order differential equation

which is uniquely specified by a natural frequency and damping

factor. By adjusting the natural frequency and damping factor,

and assuming a maximum permissible displacement, the best fit to

the acceleration-time tolerance curve is obtained.

Since the MSG and J-Tolerance criteria are both very similar

to EDI, they are not discussed here.

The HIC, essentially a modification of the S.I., is given by

HIC = (t^ - t^)

2.5

(a/g^) dt (seconds) (2)

where t^ and t2 are two points in time whose selection rules are

specified [48].

All of the above menti

translat ional acceleration,

rotational motion may be

injury. Moreover, unless the

center of rotation of the he

to rotate. Although some

experimenting with animals

head injury, have shown that

may be produced by impact-in

little has been done to estab

accelerat ion

oned criteria

As discussed e one of the c line of impac

ad, all impact

investigato

to study the

under certain

duced rotation

lish tolerance

are for impact-induced

arlier, impact-induced

auses of internal head

t passes through the

s would cause the head

rs [2] and [l6],

mechanism of internal

conditions an injury

alone, yet relatively

limits for rotational

Ommaya et al . [36] obtained a rotational acceleration-time

tolerance curve for whiplash injury and cerebral concussion for

monkeys. They also obtained a scaling relationship between subhuman primates and man for concussive levels of rotational

acceleration, and concluded that the human should have greater

than a 99% probability of concussion at an angular acceleration

of 7500 rad/s ^ with impact pulse duration exceeding 6,5

milliseconds

Suggested threshold values for life-threatening concussions

or internal head injury are given in Table 2. Threshold values

for other internal head injuries and non-life threatening

concussion have not been found.

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Present Standards for Helmets

The first performance standard for crash helmets for racing

drivers was published by Snell Memorial Foundation in 1959. It

was revised and made more stringent in 1962, and again in 1968,

as the state-of-the-art of helmet manufacture advanced. The

Foundation published a newer Standard for Protective Headgear

which became effective July 1, 1970. This Standard is even more

demanding in its test requirements [49]. It specifies methods to

test the impact energy attenuation properties of the helmet

assembly, shell penetration resistance, and the strength of the

retention system and its attachment. The impact energy

attenuating (shock-absorbing) properties of the helmet assembly

are tested as follows: The helmet to be tested is placed on a

standard headform containing an acceleration transducer at its

center of gravity and the headform assembly is dropped from a specified height, in a specified orientation, onto a steel anvil.

The transducer output is recorded as a function of time. If the

recorded acceleration is less than specified limits for a

specified time duration, the helmet is assumed to be adequate.

Details of the test equipment and test procedures are found in

the Standard [49].

The American Standards Association, in 1966, published the

ASA Z90. 1-1966 standard requiring the same level of protection

against impact as required in the 1962 Snell Memorial Foundation

standard. The test equipment and the test procedures specified

in the present form of this standard, known as ANSI Z90. 1-1971

American National Standard Specifications for Headgear for

Vehicular Users [50], are identical to those of the Snell

Memorial Foundation 1970 standard. However, the performance

requirements of the ANSI Z90, 1-1971 standard, especially with

respect to the energy-absorbing capability of the helmet, are

less demanding, because the tests are conducted with lower impact

energies and greater induced accelerations are acceptable.

The safety standard proposed by the National Highway Traffic

Safety Administration for motorcycle helmets [51] is a

modification of the ANSI Z90. 1-1971 standard. The major

difference is the criterion for adequate energy-absorbing

performance. Instead of peak acceleration and time duration

above a specified acceleration, the criterion used in this

standard is a specified value of HIC (equation 2), calculated

from characteristics of the acceleration pulse obtained from the

drop test. If the calculated HIC is less than 1000 seconds the

test helmet is assumed to be satisfactory. Details are given in

reference [51].

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Rayne and Maslen [52] in I969, suggested methods to evaluate

buffet helmets. I.e. helmets used to protect against repeated

low-energy Impacts. Their suggested test method, similar to that

specified in the ANSI Z90. 1-1971 standard, is conducted with an

impact energy of 22.5 foot-pounds-force (30.6 Joules); the

maximum acceleration acceptable is 120 .

The preliminary standard for hockey helmets, published in

January 1973 by the Canadian Standards Association [53] > is a

modified version of the American National Standard Safety

Requirements for Industrial Head Protection (ANSI Z89. 1-1969),

which was published on December 17> 1969 [5^]. The test

equipment and test procedures do not appear to be applicable to

athletic helmets.

The Law Enforcement Standards Laboratory of the National

Bureau of Standards is developing safety standards for riot

police helmets, and Committee F-8 of the American Society for

Testing and Materials (ASTM) is developing safety standards for

football helmets. The test methods proposed by both of these

organizations are similar to those described in the ANSI Z90.1-

1971 Standard. However, certain changes in the test equipment,

the impact energy at which the tests are conducted, and the

performance criteria are all under review [55].

A major change considered by ASTM is a change in the test

headform. Instead of the metallic headform described in the ANSI

Z90.I-I97I Standard, a resilient headform designed and developed

at Wayne State University was considered. However, ASTM decided

not to use the resilient headform at this time and to continue

using the metallic headform because the resilient headform has

not given reproducible results during a round robin test, it is

thought to be fragile, thereby limiting the impact energy that

can be used in drops, and it is still under development [55].

Each of the present standards specifies a solid headform

without a simulated neck attachment and therefore cannot provide

information regarding impact-induced rotation of the head.

Impact-induced rotation has been identified as one of the major

causes of internal head injuries [14], [16], It may also cause

injuries to the neck area, including damage to the spinal cord,

blood vessels, and muscles and ligaments of the neck [5], [6].

Moreover, a poorly designed helmet system may actually increase

the likelihood of impact-induced head rotation, thereby

increasing the danger of neck and internal head injuries. For

example, Schneider et al. [56] claim that the use of face

protection devices which are part of the helmet system has

increased the number of injuries of the neck and spinal cord.

-12-
Although helmets are not designed to protect against neck

injuries, an effective evaluation of the overall helmet system

should include a measurement of impact-induced rotation, in order

that any additional danger of neck injuries created by the helmet

system could be verified. Obviously, protection of one part of

the body at the expense of another may not be desirable.

The performance criteria in most of the standards are based

upon life-threatening head injury. These criteria may be

adequate for crash helmets, designed to protect against a single

strong impact. In athletic events, however, the athlete should

also be protected from injury that can result from repeated

moderate or intermediate impacts. Therefore, the performance

criteria and test conditions developed for crash helmets may not

be appropriate for athletic helmets.

Performance Criteria for Athletic Helmets

To develop effective performance criteria, one should have a

clear understanding of the type and severity of head injuries

which are unacceptable. From impact tolerance curves and injury

threshold data, one could then determine the maximum acceptable

impacts that may be received by the head. Unfortunately, injury

threshold data for sub-fatal internal head injuries are not

available, yet such injuries, including sub-fatal concussion, are

among the most common head injuries suffered by helmeted

athletes

The other important information required for helmet

performance criteria concerns the impact conditions that are

generated in athletic accidents, such as the ranges of impact

energy and velocity, regions of the head impacted, geometry of

the object contacted. Although some investigations have been

conducted in the past to study head injuries occurring in certain

sports [56], [57], [58], [59]> and to determine the translational

accelerations experienced by football players during competition

[60], [61], systematic assessment of impact conditions has

received little attention. Impact conditions differ from one

sport to another. To be effective, performance criteria and test

procedires must be specific for the impact conditions of each

sport

To determine the types and severities of head injuries which

are unacceptable, to assure the adequacy and reproducibility of

test equipment and to obtain other needed information, the

studies indicated below are recommended.

1. Consensus . Determining the types and severities of head

injuries v;hich are unacceptable is extremely difficult,

-13-
primarily because many subjective questions must be resolved.

For a conclusive settlement of this problem, a consensus of

medical experts, parents, athletes, coaches, trainers, and

team physicians, should be obtained by means of a carefully

planned survey.

.2. Case and field studies . An in-depth study should be made

of athletic accidents that have resulted in head injuries.

These studies should investigate factors such as the cause

of the accident, state of mind of the athletes Involved

prior to the accident, type and severity of injuries

inflicted, impact conditions of the accident, and the

objects contacted. In addition to the accident itself,

environmental conditions to which the athletes are subjected

during the competition should also be studied.

Tools to accomplish these objectives may Include motion

pictures of games, and interviews with athletes, coaches,

and team physicians. Such studies will require the

cooperation of the coaches and trainers, physicians, and

sport organizers.

3. Threshold values for sub-fatal internal head injuries . Investigations are needed to establish the threshold values

for sub-fatal internal head injuries. Such studies may

require a team consisting of neurologists, pathologists,

neurosurgeons, and engineers and adequate laboratory

facilities for experiments v/ith live animals and human

cadavers. Investigators such as Hodgson [13] and Ommaya

[16] did obtain data for impact-induced sub-fatal internal

head injuries sustained by experimental animals. Further

investigations would yield additional information, which

when combined with the presently available data could

determine the threshold values for sub-fatal internal

head injuries in humans.

^ . Calibration of test headform with respect to injury . Research should be undertaken to calibrate the test headform

and to establish the relationships between the response of

the headform to impact and probable human injury due to

similar impact. A team of Investigators and laboratory

facilities similar to those required for study 3, above,

would be needed.

A procedure for development of the desired relationships is

as follows: The headform and the intact cadaver head should

be subjected to a series of identical impacts with impactors

having a range of masses and geometric characteristics, and

using a range of impact velocities. The data will consist

-14-
of the mechanical responses of the test headform and the

cadaver head, and appraisal of the damage to the cadaver

head for each Impact. Mechanical quantities of interest are

impulse, acceleration-time history, and peak force.

The data obtained from impact experiments should be used to

develop the relationships between the responses to impact of

the test headform and of the cadaver head. A second

relationship between the cadaver head response and live

human injury should be developed. The data obtained in the

impact experiments, injury data in the literature, and data

collected for sub-fatal internal head injuries in study 3>

may be useful for developing the second relationship.

These two relationships would then be combined to yield the

correspondence between test headform response and probable

human injury. Thereafter, similar test headforms could be

calibrated using the data already developed,

5 . Test Equipment

A round robin test program should be designed and

undertaken to make certain that participants interested

in helmets are capable of obtaining equivalent results.

Before launching a program to develop new test headforms

the possibility of using the ANSI Z90.1 headform, with

or without modifications, or the resilient headform

developed at Wayne State University, or the resilient

head-neck system developed at the Highway Safety

Research Institute, University of Michigan, should be

thoroughly explored.

6. Interim standards . The efforts essential for effective

standards for athletic helmets are involved and may

take a long time to complete. Hov/ever, helmet safety

standards, especially for amateur athletes and children,

are badly needed. By making the best use of current

information, an interim performance standard for

athletic helmets should be developed. As the state

of the art advances, the interim standard can be

appropriately revised.

-15-
Concluding Remarks

It Is difficult, at present, to establish effective

performance criteria for athletic helmets because most of the

needed information is not yet available. Vital Information, such

as threshold values for sub-fatal head injuries, is hard to

obtain because humans are complex and variable, and techniques

for testing live humans are limited. Nevertheless, by careful

use of available Information, interim performance criteria and

standards for evaluating athletic helmets can be developed. An

Interim standard will have to suffice until the essential

information becomes available.

-16-
References

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,

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-17-
12. Hodgson, V. R. , Thomas, L. M. , Gurdjlan, E. S,, Fernando, 0.

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680053, 1968.

-18-
25. Gadd, C. W., "Use of Weighted-Impulse Criteria for

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28. Hodgson, V. R., Thomas, L. M. and Prasad, P., "Testing the

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29. Hodgson, V, R. and Patrick, L. M., "Dynamic Response of the

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30. Koenhauser, M, and Cold, A., "Application of Impact

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31. Master, B. G., and Saczalski, K. J., "Anthropomorphic

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32. Melvin, J. W. and Evan, F. G, "A Strain Energy Approach to

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33. Melvin, J. W., Fuller, P. M. , Daniel, R. P. and Pavliscak,

G. M., "Human Head and Knee Tolerance to Localized Impact."

S.A.E. Paper No. 690477, I969.

34. Nahum, A. M., Gatts, J. D. , Gadd, C. W, and Danforth, J.,

"Impact Tolerance of the Skull and Pace." Proc. 12th Stapp

Car Crash Conf., S.A.E. , I968.

35. Ommaya, A. K. and Hirsch, A. E., "Tolerance for Cerebral

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Biomechanics, 4, 197I (13-21).

36. Ommaya, A. K., Yarnell, P., Hirsch, A. E. and Harris, E. H.

,

"Scaling of Experimental Data on Cerebral Concussion in Subhuman Primates to Concussion Threshold for Man." NIH,

670906, 1967.

-19-
37. Patrick, L. M. , "Human Tolerance to Impact - Basis for

Safety Design." S.A.E. Paper 650171, 1965.

38. Slattenschek, A. and Tauff kirchen, W. , "Critical Evaluation

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,

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m. Stalnaker, R. L., McElhaney, J. H. "Head Injury Tolerance

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Paper No. 70-WA/BHF-21 , 1970.

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Thomas, 1970.

43. States, J. D., "The Abbreviated and Comprehensive Research

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44. Gadd, C. W., Peterson, F. J., and Lange , W. A., "Strength of

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45. Deck, J. D., "Skin Histology and the Effect of Injury - unpublished data." Personal communication, University of

Virginia, School of Medicine, 1972.

46. McGuire, B, J., Sorrells, J. R. and Moore, J. D.,

"Resistance of Human Skin to Puncture and Laceration." NBS

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Related to Motor Vehicle Design - SAE J885a, SAE Handbook,

1973.

48. Department of Transportation National Highway Traffic Safety

Administration (49 CFR Part 571) Docket No. 69-7, Notice 17,

"Occupant Crash Protection Head Injury Criteria." Federal

Register, Vol. 37, No. 52 March 16, 1972.

-20-
^9 ' "standard for Protective Headgear." Snell Memorial

Foundation. 1970.

50. "American National Standard Specif i-^at ions for Protective

Headgear for Vehicular Users." ANSI Z90. 1-1971, American

National Standards Institute, Inc., 1971.

51. Motorcycle Helmets, Proposed Motor Vehicle Safety Standard

(i\9 CFR Part 571), Docket No. 72-6, Notice 1, National

Highway Traffic Safety Administration.

52. Rayne, J. M. and Maslen, K. R. , "Factor in the Design of

Protective Helmets." Aerospace Medicine, June I969.

53. Hockey Helmets, CSA Preliminary Standard Z262. 1-1973

Canadian Standards Association, 1973. Canadian Standards

Association, 1973.

5^1. American National Standard "Safety Requirements for

Industrial Head Protection", ANSI Z89.I-1969, American

National Standards Institute, Inc., Dec. 17, 1969.

55. Personal Communication.

56. Schneider, R. C, et al., "Serious and Fatal Football

Injuries Involving Head and Spinal Cord." JAMA 177, 1961

(362-367).

57. Robey, J. M. Blythe, C. S and Mueller, F. 0., "Athletic

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1971, (184-189).

58. Politho, N., "Head Injuries in Ice Hockey at the Amateur

Level." M. S. Thesis, University of Wisconsin, Madison,

Wis. , 1970.

59. Toogood, T. and Love, W. G,, "Hockey Injury Survey."

Canadian Association of Hockey Players Journal, Dec. I965,

Jan. 1966.

60. Moon, D. W. , Beadle, C. W. and Kobacic, C. R., "Peak Head

Acceleration of Athletics During Competition - Football."

University of California, Davis, California, July 1970.

61. Reid, S. E, Tarkington, J. A. and Healion, T. E., "Radio

Telemetry in the Study of Head Impacts in Football." Proc

5th National Conference on the Medical Aspects of Sports,

AMA, 1963.

-21-
62. National Commission on Product Safety Final Report, to the

President and Congress of the United States, June 1970.

-22-
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Figure I. Schematic Anatomy of Human Head
NBS-1 14A (REV, 7-73)

U .S. DEPT. OF COMM. BIBLIOGRAPHIC DATA

SHEET

1. I'HHI.K A riON OK KM'OK 1 NO. NBSIR 73-276

2. ( UIV 'i Acre s s ion No.

3. Kci ipieiii 's Al l c-.s.'.ioii No.

•t. I I 1 1,1. AINW t 1 l-l. Standards for Athletic Helmets — State of the

Art and Recommendations

5. I'uhliealiim Date May 197^

6« 1 frftirmiii^ Or^iini/'. iition ^ otlf

7. AUTHOR(S)

Bal M. Mahajan

8. Performing Or^an. Report No. NBSIR 73-276

9. PKRI-'ORMINC; ORGANIZATION NAME AND ADDRIiSS

NATIONAL BUREAU OF STANDARDS

DEPARTMENT OF COMMERCE

"AorllNulUN, U.C zUzJ4

10. Proirit/Task,/Work Unit No. ^460505

11. Contract /Clrant No.

12. Sponsoring Organization Name and C'omplete Address (Street, City, State. ZIP)

Consumer Product Safety Commission

5^01 Westbard Ave.

Bethesda, Md. 20016

13. Type of Report & Period Covered p^y^al

4/73 to 8/73

14. sponsoring Agency ( odi15. SUPPLEMENTARY NOTES

16. ABSTRACT" (A 200-word or less (actual summary of most significant information. If document includes a significant

bibliography or literature survey, mention it here.) The literature pertaining to impact-induced head injuries was surveyed to

collect information concerning various types of head injuries, their

relative severity, and suggested threshold values for these injuries.

The search revealed that such threshold values are either unavailable or

questionable.

The review of the performance standards for helmets revealed that there

are no satisfactory performance standards available for athletic helmets

and that the performance criteria and testing procedures presently

employed to evaluate helmets may be neither applicable to nor adequate

for the testing of athletic helmets.

Information is suggested that is considered necessary for the development

of performance criteria and test procedures for meaningful evaluation of

athletic helmets. Pertinent studies required for the acquisition of such

information are suggested. Since some of these studies are complex and

may take a long time to complete, it is suggested that interim performance standards for athletic helmets be developed utilizing presently

available information, and that these standards be revised "as the stateQf-thp-art advances.

17. KEY WORDS (six to twelve entries; alphabetical order; capitalize only the first letter of the first key word unless a proper name; separated by semicolons

)

Athletic helmets; injury criteria; head injury; protective helmets;

impact injury; cranial concussion

18. AVAILABILITY Unlimited 19. SECURITY CLASS

(THIS REPORT)

21. NO. OF PAGES

For Official Distribution. Do Not Release to NTIS

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20. SEC:URITY CLASS

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22. Price

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USCOMM-DC 29042-P74